Father-son relationships can be complex enough without the added strains of fame, fortune and a father's philandering.

Throw those elements into the mix, and you've got something resembling the connection between Kirk and Michael Douglas. The new HBO documentary "A Father . . . a Son . . . Once Upon a Time in Hollywood" details the personal lives (and past conflicts) of the well-known Hollywood duo.

Zap2it spoke to the pair about the documentary from the elder Douglas's home in Beverly Hills, Calif., on the night after the documentary's premiere screening.

You're both so well-acquainted with director Lee Grant. Was that a factor in your comfort in talking so freely about your relationship?

Michael: Lee Grant was blacklisted at a key point in her life. She did "Detective Story" with Dad, and she and her insane, lovely, wacky husband -- Joe Feury -- have been great friends of ours for many years. A lot of the interview was done at their house, and Joey kept seducing Dad with a lot of good food. There was a trust factor unique with Lee that allowed us to feel we could talk.

Kirk: Filming the documentary was wonderful, because we both forgot about the camera and just started talking like father and son.

It's interesting how the program opens by recalling the casting of "One Flew Over the Cuckoo's Nest" (the 1975 movie that earned Michael an Oscar for producing after Michael gave Jack Nicholson the role Kirk had long coveted). Even this many years later, do the related emotions surprise you as much as it seems?

Kirk: Of course! You see, I'm so proud of Michael for doing something that I had attempted to do for 10 years. Within a few months, he got together a great cast, and the results are history.

Michael: Look, I know what a great part and what a great movie it was. I think it's only right and fair that it should be the issue it was, but love conquers all, and life goes on.

Much is made in the documentary about Kirk's eye for women. Were you both surprised at the honesty of Kirk's ex-wife and current wife's remarks about that?

Kirk: I was shocked!

Michael: I know you were. That was one of the things at the screening, Dad, that so many people picked up on. It's too bad so many families can't talk to each other about issues, instead of keeping silent. One thing that isn't brought out so much in the film is that I've been blessed with great step-parents. In families of divorce, when the adults can get together, there are fewer problems.

Is it an accurate impression that some of your strongest personal ties have been to other stars?

Michael: You know what took the house down last night, Dad? You and Burt [Lancaster] singing "It's Great Not to Be Nominated" [in a late-1950s Academy Awards show]. Seeing you two guys do that was really incredible.

Kirk: I miss Burt. He always said, "Kirk would be the first to admit he's a very difficult man. I would be the second." We did so many things together; we even did a song-and-dance routine at the London Palladium. We could have made lots of money in vaudeville.

Michael: I think the friendships of Dad's generation lasted a lot longer, but a lot of it just had to do with geography. A lot of the industry was here; if you made movies, you were in Hollywood. Now, we can live all over the world because pictures are made everywhere. It was a much closer community back then.